Use iterators to avoid calculating all properties of UnionOrIntersectionType

src/compiler/checker.ts

@@ -183,6 +183,7 @@ import {
     findAncestor,
     findBestPatternMatch,
     findIndex,
+    findIterator,
     findLast,
     findLastIndex,
     findUseStrictPrologue,
@@ -948,6 +949,7 @@ import {
     skipTrivia,
     skipTypeChecking,
     some,
+    someIterator,
     SourceFile,
     SpreadAssignment,
     SpreadElement,
@@ -1239,6 +1241,7 @@ const enum TypeSystemPropertyName {
     ResolvedBaseTypes,
     WriteType,
     ParameterInitializerContainsUndefined,
+    ResolvedProperties,
 }
 
 /** @internal */
@@ -10127,6 +10130,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 return !!getSymbolLinks(target as Symbol).writeType;
             case TypeSystemPropertyName.ParameterInitializerContainsUndefined:
                 return getNodeLinks(target as ParameterDeclaration).parameterInitializerContainsUndefined !== undefined;
+            case TypeSystemPropertyName.ResolvedProperties:
+                return !!(target as UnionOrIntersectionType).resolvedProperties;
         }
         return Debug.assertNever(propertyName);
     }
@@ -13465,26 +13470,70 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function getPropertiesOfUnionOrIntersectionType(type: UnionOrIntersectionType): Symbol[] {
-        if (!type.resolvedProperties) {
-            const members = createSymbolTable();
-            for (const current of type.types) {
-                for (const prop of getPropertiesOfType(current)) {
-                    if (!members.has(prop.escapedName)) {
-                        const combinedProp = getPropertyOfUnionOrIntersectionType(type, prop.escapedName);
-                        if (combinedProp) {
-                            members.set(prop.escapedName, combinedProp);
+        for (const _ of iteratePropertiesOfUnionOrIntersectionType(type, /*doYield*/ false)) {
+            Debug.fail("Iterator should have been empty.");
+        }
+        return type.resolvedProperties!;
+    }
+
+    function* iteratePropertiesOfUnionOrIntersectionType(type: UnionOrIntersectionType, doYield = true) {
+        if (type.resolvedProperties) {
+            if (doYield) {
+                yield* type.resolvedProperties;
+            }
+            return;
+        }
+
+        if (doYield && type.partiallyResolvedProperties) {
+            yield* type.partiallyResolvedProperties;
+        }
+
+        if (!pushTypeResolution(type, TypeSystemPropertyName.ResolvedProperties)) {
+            return;
+        }
+
+        // If we have a generator already, pick up where we left off.
+        // Otherwise, we haven't started, so create a new one.
+        try {
+            const generator = type.partiallyResolvedPropertiesGenerator ??= iteratePropertiesOfUnionOrIntersectionTypeWorker(type);
+            for (const symbol of generator) {
+                type.partiallyResolvedProperties = append(type.partiallyResolvedProperties, symbol);
+                if (doYield) {
+                    yield symbol;
+                }
+            }
+        }
+        finally {
+            // Ensure we pop when we're all done iterating. If done outside of a finally,
+            // this code won't actually execute.
+            popTypeResolution();
+        }
+
+        type.resolvedProperties = type.partiallyResolvedProperties ?? emptyArray;
+        type.partiallyResolvedProperties = undefined;
+        type.partiallyResolvedPropertiesGenerator = undefined;
+    }
+
+    function* iteratePropertiesOfUnionOrIntersectionTypeWorker(type: UnionOrIntersectionType) {
+        const seenSymbols = new Set<__String>();
+        for (const current of type.types) {
+            for (const prop of getPropertiesOfType(current)) {
+                if (!seenSymbols.has(prop.escapedName)) {
+                    const combinedProp = getPropertyOfUnionOrIntersectionType(type, prop.escapedName);
+                    if (combinedProp) {
+                        seenSymbols.add(prop.escapedName);
+                        if (isNamedMember(combinedProp, prop.escapedName)) {
+                            yield combinedProp;
                         }
                     }
                 }
-                // The properties of a union type are those that are present in all constituent types, so
-                // we only need to check the properties of the first type without index signature
-                if (type.flags & TypeFlags.Union && getIndexInfosOfType(current).length === 0) {
-                    break;
-                }
             }
-            type.resolvedProperties = getNamedMembers(members);
+            // The properties of a union type are those that are present in all constituent types, so
+            // we only need to check the properties of the first type without index signature
+            if (type.flags & TypeFlags.Union && getIndexInfosOfType(current).length === 0) {
+                break;
+            }
         }
-        return type.resolvedProperties;
     }
 
     function getPropertiesOfType(type: Type): Symbol[] {
@@ -14136,7 +14185,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         else if (type.flags & TypeFlags.Intersection) {
             if (!((type as IntersectionType).objectFlags & ObjectFlags.IsNeverIntersectionComputed)) {
                 (type as IntersectionType).objectFlags |= ObjectFlags.IsNeverIntersectionComputed |
-                    (some(getPropertiesOfUnionOrIntersectionType(type as IntersectionType), isNeverReducedProperty) ? ObjectFlags.IsNeverIntersection : 0);
+                    (someIterator(iteratePropertiesOfUnionOrIntersectionType(type as IntersectionType), isNeverReducedProperty) ? ObjectFlags.IsNeverIntersection : 0);
             }
             return (type as IntersectionType).objectFlags & ObjectFlags.IsNeverIntersection ? neverType : type;
         }
@@ -14191,12 +14240,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function elaborateNeverIntersection(errorInfo: DiagnosticMessageChain | undefined, type: Type) {
         if (type.flags & TypeFlags.Intersection && getObjectFlags(type) & ObjectFlags.IsNeverIntersection) {
-            const neverProp = find(getPropertiesOfUnionOrIntersectionType(type as IntersectionType), isDiscriminantWithNeverType);
+            const neverProp = findIterator(iteratePropertiesOfUnionOrIntersectionType(type as IntersectionType), isDiscriminantWithNeverType);
             if (neverProp) {
                 return chainDiagnosticMessages(errorInfo, Diagnostics.The_intersection_0_was_reduced_to_never_because_property_1_has_conflicting_types_in_some_constituents,
                     typeToString(type, /*enclosingDeclaration*/ undefined, TypeFormatFlags.NoTypeReduction), symbolToString(neverProp));
             }
-            const privateProp = find(getPropertiesOfUnionOrIntersectionType(type as IntersectionType), isConflictingPrivateProperty);
+            const privateProp = findIterator(iteratePropertiesOfUnionOrIntersectionType(type as IntersectionType), isConflictingPrivateProperty);
             if (privateProp) {
                 return chainDiagnosticMessages(errorInfo, Diagnostics.The_intersection_0_was_reduced_to_never_because_property_1_exists_in_multiple_constituents_and_is_private_in_some,
                     typeToString(type, /*enclosingDeclaration*/ undefined, TypeFormatFlags.NoTypeReduction), symbolToString(privateProp));
@@ -22378,7 +22427,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         function membersRelatedToIndexInfo(source: Type, targetInfo: IndexInfo, reportErrors: boolean, intersectionState: IntersectionState): Ternary {
             let result = Ternary.True;
             const keyType = targetInfo.keyType;
-            const props = source.flags & TypeFlags.Intersection ? getPropertiesOfUnionOrIntersectionType(source as IntersectionType) : getPropertiesOfObjectType(source);
+            const props = source.flags & TypeFlags.Intersection ? iteratePropertiesOfUnionOrIntersectionType(source as IntersectionType) : getPropertiesOfObjectType(source);
             for (const prop of props) {
                 // Skip over ignored JSX and symbol-named members
                 if (isIgnoredJsxProperty(source, prop)) {

src/compiler/core.ts

@@ -177,6 +177,21 @@ export function find<T>(array: readonly T[] | undefined, predicate: (element: T,
     return undefined;
 }
 
+/** @internal */
+export function findIterator<T>(iter: Iterable<T>, predicate: (element: T, index: number) => boolean, startIndex = 0): T | undefined {
+    let i = 0;
+    for (const value of iter) {
+        if (i >= startIndex) {
+            if (predicate(value, i)) {
+                return value;
+            }
+        }
+        i++;
+    }
+    return undefined;
+}
+
+
 /** @internal */
 export function findLast<T, U extends T>(array: readonly T[] | undefined, predicate: (element: T, index: number) => element is U, startIndex?: number): U | undefined;
 /** @internal */
@@ -680,6 +695,16 @@ export function some<T>(array: readonly T[] | undefined, predicate?: (value: T)
     return false;
 }
 
+/** @internal */
+export function someIterator<T>(iter: Iterable<T>, predicate: (value: T) => boolean): boolean {
+    for (const v of iter) {
+        if (predicate(v)) {
+            return true;
+        }
+    }
+    return false;
+}
+
 /**
  * Calls the callback with (start, afterEnd) index pairs for each range where 'pred' is true.
  *

src/compiler/types.ts

@@ -6415,13 +6415,17 @@ export interface UnionOrIntersectionType extends Type {
     /** @internal */
     propertyCacheWithoutObjectFunctionPropertyAugment?: SymbolTable; // Cache of resolved properties that does not augment function or object type properties
     /** @internal */
-    resolvedProperties: Symbol[];
+    resolvedProperties?: Symbol[];
     /** @internal */
-    resolvedIndexType: IndexType;
+    resolvedIndexType?: IndexType;
+    /** @internal */
+    resolvedStringIndexType?: IndexType;
+    /** @internal */
+    resolvedBaseConstraint?: Type;
     /** @internal */
-    resolvedStringIndexType: IndexType;
+    partiallyResolvedProperties?: Symbol[];
     /** @internal */
-    resolvedBaseConstraint: Type;
+    partiallyResolvedPropertiesGenerator?: Generator<Symbol, void>;
 }
 
 export interface UnionType extends UnionOrIntersectionType {